Internally expanding brake



F. R. COWELL INTERNALLY EXPANDING BRAKE Mayl, 1944.

5 sheets-Sheet 1 Filed Aug. 20, 1942 F. R. COWELL INTERNALLY EXPANDING BRAKE May 16, 1944.

Filed Aug. 20, 1942 ,131 32 i@ 4 21 'Ml -ffn 5 Sheets-Sheet 2 www i May 16, w44. F. R. .cowELLA INTERNALLY EXPANDING BRAKE Filed Aug. 20, 1942 3 Sheets-5h69?I 3 Patented May 16, 1944- NTERNALLY EXPANDING BRAKE Frederick Raymond Cowell, Leeds, England, as-

signor to Kirkstall For land Application August zo, 1942, serial No.

` InGreat Britain September 4, 1941 Claims.

. In U.,S. Patent No. 2,271,8151 have described various forms of internally expanding brakes designed to provide an effective braking surface extending around substantially the whole of the periphery of the brake drum and to obtain a ge Limited, Leeds, Eng- (Cl. 18S-78) l but showing the expander and brake adjuster in uniform distribution of braking pressure over the contacting st lriacesA of the brake shoes and the drum. .f l Y In all the constructions described in the abovementioned earlier U. S. patent, the brake is of the type comprising a pair of brake-shoe-carriers which are normally held inoperative and which move outwardlyto apply the brake, each carrier 4supporting a pair of brake shoes, both of which-are arranged to present one end to the elevation, Fig. 3 is a sectional view similar to Fig. 1, but showing the brake on andthe linings worn,

,Fig. 4 is 'a section onthe line IV-IV in Fig. l, Fig. 5 is ya sectional view, similar to Fig. 1 but with the brake on, showing the second arrangement, and

Fig. 6 is a section on'the line VI-,VI in Fig. 5. Like reference numerals indicate like parts throughout the gures.

brake drum before the other on outward movement of the carrier and are free to move circumferentially'with lrespect to the carrier to a limited extent when contacted by the revolving brake drum, and ymeans operative on circumferential movement of the's'hoesas aforesaid to tilt the shoes in relation to the carrier so as to approach 'the remote Aends of the shoes towards the drum, therebyequalising the' braking pressure over the contacting faces of the shoes and the drum.

The present invention 'provides a simplified arrangementl for' achieving the same result, which is cheaperto produce; The invention Aprovidesanl internally expanding brake of the above type, whichincludes stop means operatingon Contact of the shoes with the revolving brake drum', to arrest the trailing shoe "on eachcarrierwhile maintaining its front `@anni brakingepntact withthedrom, the from; end ofrgthe leading shoeV on each carrier being brought, bythe frictional drag of the drum, into abutment with the rear end of the trailing shoe on the othercarrier, thereby tilting all of the shoes towbring theirabutting ends into closer engagement with' the drum.

Preferably the stop means is Aconstituted by a pair of stops, located vrespectively between the adjacent ends of theshoes on the two carriers, and lying in theV path of the trailing shoes.

,Two alternative forms of internally expe-nolineT brake according to the invention,Y for use in a motor vehicle, will now be described in further detaiLby way of example. with reference to the accompanying drawings in which;-

Fig. 1 is avertical section through the brake drum of the first arrangemennshowing the brake on? and with new linings. v

Fig, 2 is afsection on the line II-II in Fig. l,

,Referring first of all to the arrangement shown in Figs. 1-4, the two carriers I0, which are of approximately semicircular form, are pivoted at one end on anchor pins I I carried by a brake adjuster I2 which is operable, in kknown manner, and as described in U. S. Patent No, 2,271,815, to space the anchor pins further apart for the pur-V pose of counteracting wear on the brake linings I3.A Between the free ends of the carriers is arranged'an expander I4, which is operable, also as described in U. S. Patent No. 2,271,815, to force the carriers outwardly about their pivots to apply the brake against the action of springs I5 interconnecting the carriers.

As shown in Fig. 2, each carrier I0 consists of two spaced plates I5, which are pinched together at their opposite ends to coact with the anchor pins I I of the brake adjuster and with the plunger I 1 of the expander. Each anchor pin I has a cylindrical head, formed with an axially extending groove, the inner edge of which is defined by the arcuate line I8, the end of the carrier, which is correspondingly slotted,'being tted into this groove.. The plungers Il of the expander are slotted to receive the ends of the carriers.

Each brake shoe is formed of a pair of spaced plates Ztl, located inside the plates I6 of the carrier. The plates 20 are pinched together at their inner ends at 2|, and are outwardly flanged attheir outer ends 22 to facilitate in the attachment 0f the lining. The inner portions 2l of the shoes coact each with a roller 23 mounted on the carrier, so as to permit the shoes to rnove circumferentially in relation to the carrier` against lthe action of springs 24 connecting the shoes to the carrier. The adjacent ends 25, 25a of the two shoes of each pair are located at about from the expander I 4, and it is these two ends which rst make contact with the brake drum 25 on application of the brake. The rollers 23 are located in the neighbourhood of the adjacent ends of the shoes. v

Between the adjacent ends 25, 25a of the two shoe |9a to abut against the rear end `29 of the y trailing shoe I9 on the other carrier. The result of the abutment of the two upper shoes shown in Fig. 1 is that a force, directed towards the right, is exerted on the end 29 of the shoe I9, so rocking the shoe clockwise on its supporting roller 23 and bringing its end 29 into closer en-v gagement with the` brake drum. There also is a reaction directed towards the left, on the end 29a of the shoe I9a which rocks the shoe I9a anticlockwise about its supporting roller 23 and thus brings its end 29a into closer engagement with the brake drum. A similar action takes place with the two lower shoes. As already explained the inner ends 2| of all the shoes first make contact with the drum on application of the brake, and thesubsequent movement of the other ends 29, 29a of the shoes into closer contact with the drumk when' the shoes are arrested by the stops, has the eiect of equalizing the braking pressure between the shoes vand the drum. It will be appreciated that this action will take place for both directions of rotation of the drum, so that when the brake is tted to a road vehicle it will bev equally effective whether the .vehicle is travelling forwards or in reverse.

As the linings become worn, the clearances between the abutting end 29, 29a of the shoes and Ybetween the shoes and the fixed stops 21 increase, so that when the linings are nearly worn out, there is likely to be a considerable shock when the brake is applied. l

To avoid this disadvantage an automatic slack adjuster is provided. This consists of a pair of wedges 30 each of which is mounted adjacent to one of the xed stops 21. stepped end,A the steps being indicated by the reference 3 I, and constitutes a forward prolongation of a plunger 32 (see Fig. 4) which is slidably mounted in a cylinder 35 formed as a unit with and extending rearwardly from the associated fixed stop 21. recess in the plunger 32 and abutting against a screw cap 3,4 which closesthe cylinder 35, tends to urge the wedge 39 in a forward direction.

When the vlinings are new, the end step 3| of the wedge 30 rests beneath the brake shoe adjoining the stop as shown in Fig. 4. As wear takes place, the wedge is forced forwards by the spring 33 until Vthe end step can move into position between the fixed stop 21 and the end 25a of the adjoining shoe, so increasing the effective width ofthe fixed stop and taking up slack. After,I more wear has taken place, the next step comes into operation and so on, until the linings are completely worn, when the last step has come intooperation and the whole width of the plunger is utilized to take up the slack between the shoe andthe xed stop, as shown in Fig. 3. The riser portion of each step A spring 33, located in a Each wedge has a 3|, which is of greater depth than the thickness of the iiattened portion 2| of the shoe, is out I 5 and 6, the arrangement is generally the same except that the stops 21 are constituted by snail cams 36 which are rotatably mounted on pins 31 fixed to the back plate 26. A helical spring V38, one end of which is tucked rearwardly into a hole in the pin 31 and the other end of which engages under the nose of the snail cam 3S, tends to turn the latter in the sense indicated by the arrows, so as to bring a widerv portion of the cam into the space betweenthe ends 25, 25*l of the shoes, in this way automatically taking up the slack as the linings wear.

On the rear end 25a of each trailing shoe III is mounted a leaf spring |25, which., being more powerful than the helical spring 38, lies parallel to the end of the shoe (as shown in Fig. 5) despite the tendency oi the snail cam 36 to press it back against the shoe. When the brake is released, however, the springs I5 will overpower the leaf springs |25, and the clearance occasioned by their deflection into contact with the ends of the shoes will be suiicient'to permit the shoes to move into the off position.

In the arrangement shown in Fig. 5 the two rollers 23 on each carrier, which serve to support the adjacent ends ofthe two shoes, are mounted on opposite ends of a link 39 which can float relatively to the carrier on'a central pivot 40. With this arrangement an equal outward thrust will be applied to the adjacent ends 25, 25a of each pair of shoes I9, I9* when the carriers are moved outwards, thereby further equalizing the braking pressure between the shoes and the drum. i

It will be understood that the carriers nee not necessarily be mounted on AYpivots as illustrated, but that the brake adjuster may be replaced by a second expander, the two expanders acting to force the carriers bodily apart to apply the brakes as described in U. S. Patent No. 2,271,815.

With the above-described arrangements not only is it possible to utilize nearly the whole periphery of the drum for braking and to equalise the braking pressure between. the shoes and the drum, but a self-energizing eiect is obtained, the reaction of the eifort Whichforces the remote ends 29, 29H of the shoes against the drum being taken on the xed stops and not resisting the drivers eiort in applying the Ibrakes.

I am aware that a brake has been proposed having two shoes on each carrier, each shoe be` ing mounted centrally on a roller, on which it can pivot to equalize the braking pressure-.over the surface of the shoe. In this construction the adjacent ends of the two shoes on each carrier were arranged to abut against one another and xed stops, located in the vvicinity of the pivots and of the expander, were provided for the purpose of arresting the shoes. My invention is distinguished from this arrangement in two important respects. In the first place I arrange for the stop means to arrest the trailing shoes on the two carriers, and not the leading shoes as do the stops of this prior proposal, and arrange for the leading shoe on each carrier to abut against the trailing shoe on the other carrier instead of making the two shoes on the same carrier abut against one another. In the second place, I arrange for the initial braking pressure, due to the outward movement of the carriers to be applied to one end of each shoe and the self-energizing pressure due to the stop means to be applied to the other ends of the shoes; instead of applying the initial braking pressure centrally of the shoes as in the known arrangement.

Although the invention has been described mainly with reference to its application to brakes for motor road vehicles, it is to be understood that it may equally well be used in internally expanding brakes for other purposes.

What I claim as my invention and desire to secure by Letters Patent is:

l. An internally expanding brake, comprising a brake drum, a pair of brake-shoe-carriers mounted within the drum, means for retaining the carriers in an inoperative position, an expander for moving the carriers outwardly to apply the brake, a pair of brake shoes mounted on each carrier, a pair of rollers on each carrier supporting the adjacent ends of the two shoes and, permitting of circumferential movement of the shoes in relation to the carrier, a floating link on each carrier carrying the rollers at its ends and pivoted centrally to the carrier, all of the brake shoes being arranged to present one end to the brake drum before the other on outward movement of the carriers and stop means operating, on circumferential movement of the shoes when contacted by the revolving brake drum, to arrest the trailing shoe on each carrier while maintaining its front end in braking contact with the drum, and thereby causing al1 of the shoes to tilt, on the subsequent abutment of the front end of the leading shoe on each carrier with the rear end of the trailing shoe on the other carrier, to bring their said abutting ends into closer engagement with the brake drum.

2. In an internally expanding brake, in combination, a brake drum, two brake shoe carriers mounted within the drum, means normally maintaining the carriers in inoperative position, an expander for moving the carriers outwardly to apply the brake, a leading brake shoe and a trailing brake shoe mounted on each carrier, the brake shoes being so arranged on the carriers that the front end of the leading shoe of one carrier may engage the rear end of the trailing shoe of the other carrier when said shoes are in engagement with the drum, means on each Carrier for causing the adjacent ends of the two brake shoes mounted on that carrier to contact with the drum before the opposite ends of said shoes contact with said drum when the carriers are moved outwardly, and stop means to arrest the movement of the trailing shoe of each carrer upon engagement of the shoes with the drum, thereby causing the front end of the leading shoe of each carrier to abut against the rear end oi' the trailing shoe of the other carrier and these abutting ends to be brought into closer engagement with the drum when the movement of said trailing shoes is arrested by said stop means.

3. In an internally expanding brake, in combination, a brake drum, two brake shoe carriers mounted within the drum, means normally maintaining the carriers in inoperative position, an expander for movin-g the carriers outwardly to apply the brake, a leading bra-ke shoe and a trailing brake shoe mounted on each carrier, the brake shoes being so arranged on the carriers that the front end of the leading shoe of one carrier may engage the rear end of the trailing shoe of the other carrier when said shoes are in engagement with the drum, a pair of rollers on each carrier for supporting the adjacent ends of the two brake shoes mounted on that carrier for limited circumferential movement relative thereto and to cause said ends to contact with the drum before the opposite ends of said shoes contact with said drum when the carriers are moved outwardly, and stop means to arrest the movement of the trailing shoe of each carrier upon engagement of the shoes with the drum, thereby causing the front end of the leading shoe of each carrier to abut against the rear end of the trailin-g shoe of the other carrier and these abutting ends to be brought into closer engagement with the drum when the movement of said trailing shoes is arrested by said stop means.

4. In an internally expanding brake, in combination, a brake drum, two brake shoe carriers mounted within the drum, means normally maintaining the carriers in inoperative position, an expander for moving the carriers outwardly to apply the brake, a leading brake shoe and a trailing brake shoe mounted on each carrier, the brake shoes being so arranged on the carriers that the front end of the leading shoe of one carrier may engage the rear end of the trailing shoe of the other carrier when said shoes are in enga-gement with the drum, a oating link pivotally mounted centrally on each carrier, rollers mounted on the ends of each link and engaging, respectively, the adjacent ends of the brake shoes mounted on that carrier, said rollers causing the adjacent ends of the two brake shoes mounted on that carrier to contact with the drum before the opposite ends of said shoes contact with said drum when the carriers are moved outwardly, and stop means to arrest the movement of the a trailing shoe of each carrier upon engagement of the shoes with the drum, thereby causing the front end of the leading shoe of each carrier to abut against the rear end of the trailing shoe of the other carrier and these abutting ends to be brought into closer engagement with the drum when the movement of said trailing shoes is arrested by said stop means.

5. The combination set forth in claim 3 in which a spring connects each shoe to the associated carrier and opposes circumferential movement of such shoe relatively to the carrier.

FREDERICK RAYMOND COWELL. 

